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Databases

Boolean Operators

What are Boolean Operators?

Boolean operators are logical expressions used to focus your search within a database. Many academic databases are designed to retrieve the information you tell it to retrieve by using subject headings and keywords. Boolean operators are the connectors that are used to create search strategies with those subject headings and keywords.The main Boolean operators are AND, OR, NOT, and they connect your search words to either narrow or broaden the search results. 

Search order 

Databases return results based on the word terms (i.e. subject headings and keywords) and the Boolean operators used. Be aware of the order in which words are connected when using Boolean operators.

  • Databases usually recognize AND as the primary operator, and it is typically the default operator inserted between terms whenever you search with more than one term.* By default databases will connect concepts with AND together first.
  • If you use a combination of AND and OR operators in a search, enclose the words to be OR-ed together in parentheses.

The above example illustrates a command to the database that says, "Results must have 'Diet Therapy" and either contain the terms 'Bulimia' or 'Anorexia.'" This means your results would have to have Diet Therapy along with Bulimia or Anorexia or both.

 

 

If you were to type the above command into a database search, each of your results could have: all three terms (Diet Therapy, Bulimia, Anorexia); only Bulimia and Anorexia; only Bulimia and Diet Therapy; or just Anorexia. 

 

*If you use a single term in your search such as "Bulimia," the database will not insert an AND operator. However, if you enter in more than a singular term, this is called a phrase. If you want to search with the phrase, or with the words together, you typically need quotes around the phrase. For example, you would type "Diet Therapywith the quotes around the phrase. 

The operator AND is used to combine different concepts together and narrow results. Concepts combined together with AND tell the database that you are requiring each result to have both/all concepts. It requires terms to be in each result in the results list. 

For example, a search with Pollution AND Asthma would retrieve results that have both these terms in each result. 

Look at your research question

Examine your research question. The three concepts identified earlier were highlighted as seen below. 

Are anti-smoking campaigns effective interventions for e-cigarette use among high school students?

 

The three different concepts are combined together with AND.*

anti-smoking campaigns

AND

e-cigarettes

AND

high school students

*This examples does not demonstrate the use of subject headings or keywords. The tab Combining Concepts and Keywords demonstrates how subject headings and keywords are combined within individual concepts and how different concepts are then combined.

Using the OR operator expands your results. Think "or is more." It is used to connect synonymous keywords and subject headings that are representative of the individual research concept together.

Look at your research question

The three concepts identified earlier were highlighted as seen below. 

Are anti-smoking campaigns effective interventions for e-cigarette use among high school students?

 

The subject headings for concepts are combined with keywords. 

anti-smoking campaigns

Smoking Prevention OR Smoking Cessation OR smoke prevention OR smoke cessation OR smoke intervention OR anti smoke OR antismoke OR anti vape OR antivape

e-cigarettes

Electronic Nicotine Delivery Systems OR electronic nicotine delivery system OR e cigarettes OR ecigarettes OR electronic cigarettes OR vape OR JUUL
 

high school students

Adolescent OR Students OR Minors OR adolescents OR students OR high school OR secondary school OR teen OR youth

The NOT operator excludes results, and it narrows your results. The NOT operator can potentially exclude relevant results. For example, you want articles about puppies early development and exclude anything about kittens. You type in the search "puppy NOT kitten." However, there may be an article that only mentions "kitten" one time in passing, but the article is about the first three months of a puppy's development after birth. See the diagram below to better understand the NOT operator. 

Proximity operators are commands that specify the distance or the number of intermediate words between two terms. Proximity operators vary among databases. The syntax (i.e. the database's encoding language) for proximity operators can look like:

  • Pollution Near/3 Asthma
  • Pollution ADJ3 Asthma

The above examples mean you are looking for resources that have the term Asthma within three words of the term Pollution. 

Reasons for using proximity operators

1. The keyword phase has a 'stop' word in the middle of it. For example, you will not be able to search "people of color" as a phrase in many systems because the word 'of' is a stop word. This means, although you put quotation marks around your phrase, the word 'of' acts as a stop, which then makes the system search for the individual words 'people' and 'color.' It is good practice to use "people NEAR/3 color" (EMBASE syntax) or "people ADJ3 color" (MEDLINE Ovid syntax). 

2. The keywords you use have a dynamic relationship with one another that is relevant to the search. For example, you want articles about how pollution causes/exacerbates asthma. If you do a proximity search with "pollution NEAR/5 asthma" you would retrieve articles that would have the phrases "pollution induced asthma," "asthma caused by pollution," or "pollution and asthma."

 

Combining Concepts and Combining Subject Headings with Keywords

The three concepts identified earlier were highlighted as seen below. 

Are anti-smoking campaigns effective interventions for e-cigarette use among high school students?

 

Now that AND and OR have both been covered, it's time to combine our subject headings with their corresponding, synonymous keywords to put the entire search together. 

Concepts: 

  • anti-smoking campaigns
    • Subject Headings*Smoking Prevention; Smoking Cessation
    • Keywords: smoke prevention; smoke cessation; smoke intervention; anti smoke; antismoke; anti vape; antivape
  • e-cigarettes
    • Subject Headings: Electronic Nicotine Delivery Systems
    • Keywords: electronic nicotine delivery system; e cigarettes; ecigarettes; electronic cigarettes; vape; JUUL
  • high school students
    • Subject Headings: Adolescent; Students; Minors
    • Keywords: adolescents; students; high school; secondary school; teen; youth

*The above Subject Headings (SH) were derived from the MeSH database.